Process for producing rice flour and use thereof

ABSTRACT

The first object of the present invention is to provide a process for producing rice flour, which enables to process both unpolished and polished rice grains into rice flour by a single procedure on an industrial scale and inexpensively. The second object of the present invention is to provide rice flour produced by the process and uses thereof for producing bakery products and noodles. The present invention solves the above objects by providing a process for producing rice flour, which comprises the steps of soaking material rice grains in water, crushing the resulting rice grains, penetrating α,α-trehalose or maltitol into the rice grains, partially drying the resulting rice grains, and milling the partially dried rice grains; rice flours obtainable by the process; and uses thereof for producing bakery products and noodles.

TECHNICAL FIELD

The present invention relates to a novel process for producing riceflour, rice flour obtainable by the process, and its uses for bakeryproducts and noodles.

BACKGROUND ART

Recently, application of rice flour to fermented bakery products andnoodles has been highlighted because rice is highly recognized as ahealthy food. There are many suggestions for the process for producingunpolished- or polished-rice flour, which is favorable for producingbakery products and noodles as an substitute of wheat flour, usingunpolished- or polished-rice as a material.

Unpolished rice flour is generally produced by the steps of roastingunpolished rice grains without polishing, and milling the resultant intoflour. For example, a process for producing unpolished rice flour,comprising the steps of allowing to expand unpolished rice grains byheating and pressurizing, and drying and milling the resultant, wasproposed as disclosed in Japanese Patent Kokai No. 22155/88. Also, asdisclosed in Japanese Patent Kokai No. 45130/2002, a process forproducing unpolished rice flour, comprising the steps of steamingunpolished rice grains, and drying and milling the resultant, has beenproposed.

While, polished rice flour is generally produced by the steps ofpolishing unpolished rice by applying to a polisher for shaving bran,soaking the polished rice in water, and drying and milling the resultantby using various milling methods such as roll-type milling, impact-typemilling, stamp-milling, and grinding with water. “JOSHINKO”, a kind ofpolished rice flour produced by roll-type milling, and “JOYOKO”, a kindof polished rice flour produced by stamp-milling are well known.Recently, there have been proposed several processes for producingpolished rice flour, for example, a process comprising the steps ofsoaking rice grains in a solution comprising pectinase, dehydrating theresulting rice grains, milling the dehydrated rice grains to a fine riceflour, drying the flour to give a moisture content of about 15% (w/w)(hereinafter, “% (w/w)” is simply abbreviated as “%” in thisspecification), and baking the resulting flour at about 150° C. asdisclosed in Japanese Patent Kokai No. 287,652/92; a process comprisingthe steps of soaking a material rice grains in a solution comprisingenzymes such as hemicellulase, pectinase, and pectin esterase, dryingthe resulting rice grains, and milling the dried rice grains asdisclosed in Japanese Patent Kokai No. 68,468/93; and a processcomprising the steps of soaking rice grains in a solution comprisingsalts of organic acids and those with pectinase, dehydrating and dryingthe soaked rice rice grains, and milling the dried rice grains asdisclosed in Japanese Patent Kokai No. 175,636/2000.

As described above, the processes for producing rice flour (throughoutthe specification, both unpolished- and polished-rice flours may besimply called as “rice flour”) are different depending on whichunpolished-rice or polished-rice is used as a material, because theproperties of those rice grain are different. Therefore, in the case ofproducing both unpolished- and polished-rice flours, there aredisadvantages of requiring specific hardwares and processes, which aresuitable therefor, and high costs for producing them. While, a methodfor producing rice flour from both unpolished- and polished-rice using asingle process as above has been also proposed. For example, a processfor producing rice flour, comprising the steps of soaking raw ricegrains including unpolished rice into water which contains an amylase;freezing the soaked rice; and drying and milling the resultant, wasdisclosed in Japanese Patent No. 3,075,556. However, the process hasdisadvantages of requiring a process of freezing rice and a relativelyhigh cost for the production.

The present invention was accomplished to solve the above variousdisadvantages of conventional processes for producing rice flour. Thefirst object of the present invention is to provide a process forproducing rice flour, which enables to prepare unpolished- andpolished-rice into rice flours in an single method on an industrialscale and inexpensively. The second object of the present invention isto provide rice flour produced by the process and uses thereof forproducing bakery products and noodles.

DISCLOSURE OF INVENTION

To solve the above objects, the present inventors have extensivelystudied to improve a process for producing rice flour from the viewpointof using saccharides.

As a result, the present inventors found that rice flour can beunexpectedly produced from both unpolished- and polished-rice using asingle method comprising the steps of:

soaking raw rice grains as a material in water according to theconventional method;

crushing the resulting rice grains mechanically for cracking unpolishedrice grains or crushing polished rice roughly; penetrating α,α-trehalose(hereinafter, “α,α-trehalose” is abbreviated simply as “trehalose”throughout the specification) or maltitol into the crushed rice grains;partially drying the resultant; and

milling the partially-dried rice grains to form rice flour.

The present inventors also found that rice flour obtained by the processhas satisfactory properties for processing to the rice flour products,especially, for producing bakery products, and its smell of brancharacteristic of rice, is suppressed because of the incorporation oftrehalose or maltitol; and accomplished the present invention.

Therefore, the present invention solves the above object by providing aprocess for producing rice flour, comprising the steps of soakingmaterial rice grains in water, crushing the soaked rice grains,penetrating trehalose or maltitol into the resulting rice grains,partially drying the resulting rice grains, and milling thepartially-dried rice grains to form rice flour; and rice flourobtainable by the process. According to the process of the presentinvention for producing rice flour, rice flour having a satisfactoryquality and property for processing to the rice flour products,especially, for producing bakery products and noodles, can be producedinexpensively and on a large scale without freezing material ricegrains, using a single method without discriminating the material ricegrains and a conventional milling plant.

BEST MODE FOR CARRYING OUT THE INVENTION

Raw rice grains can be used in the present invention as materialsindependently of the kinds of rice such as non-glutinous rice andglutinous rice. Also, unpolished rice of waste rice grain, old rice, and“minimum-access rice” as well as selected unpolished rice; and polishedrice obtainable by polishing them can be advantageously used.Optionally, in the case of polished rice, those having various polishinggrades, for example, of 30%, 50%, and 70%, and polished rice with embryobuds can be also used as materials as well as standard polished rice. Inaddition, sprouted rice can be advantageously used as materials.

At first, raw rice grains are soaked in water for, usually, 1-24 hours,preferably, 5-16 hours. Although the water for soaking is preferable tobe fresh water, water admixed with quality-improving agents such asseasonings, colorings, reinforcements, emulsifiers, etc., can beoptionally used. It is not necessary to control water temperaturestrictly for soaking, and usually ambient temperature is selected. It isdesirable that rice grains are allowed to absorb water by soaking inwater and controlled to give a moisture content of, usually, 28% orhigher, preferably, 30-33% after soaking. Usually, in a process ofproducing rice flour, raw rice grains are washed with water to removecontaminants and impurities which adhere to them. In the process forproducing rice flour of the present invention, rice grain can be washedwith water before or after soaking in water, and the timing can beproperly selected. The moisture content of rice grains applicable to thepresent invention can be measured by the steps of milling the ricegrain, drying the resulting rice flour at 135° C. for two hours, andmeasuring the change of weight according to the drying by heating methoddescribed in the notification from Ministry of Health, Labor, andWelfare, “EISHIN No.13” (Mar. 26, 1999) “Analytical method fornutritional components on expression standard for nutrition”.

Successively, rice grains, obtained by soaking in water and washing withwater, are mechanically crushed. In the case of using unpolished ricegrains as material, it is preferable to crush unpolished rice grains tothe extent of at least causing cracks, and optionally, of crushingpartly or wholly. In the case of using polished rice grains as material,it is preferable to crush polished rice grains into a roughly crushedform. The crushing process is essential in such a case. Since unpolishedrice grain has a hard outer-layer composed of cuticle, testa, andpericarp, the penetration of trehalose or maltitol into rice grain,which is done by the following step, can not be done sufficientlywithout allowing to cause cracks in unpolished rice grain. While, in thecase of polished rice grain, it is not necessary to crush rice grain iftaking a longer time for penetrating trehalose or maltitol. However,taking account of the efficiency of penetrating trehalose or maltitol,it is preferable to crush polished rice grain roughly for increasingsurface area. Machines for crushing rice grain is not restricted as faras it can be used for such a purpose, and conventional roll-type millingmachine and roll-type machine for producing noodles can beadvantageously used without special tuning. It is preferable to adjustthe slit width of the roll for crushing to 1-2 mm in the case ofunpolished rice grains, and to 2-3 mm in the case of polished ricegrains. By the above procedure, unpolished rice grains are cracked,whereas polished rice grains are roughly crushed.

Successively, trehalose or maltitol is penetrated into the crackedunpolished rice grains or the roughly crushed polished rice grains,obtained by the above crushing process. Concretely, trehalose ormaltitol, in an amount of, usually, 3-20%, preferably, 8-15%, on a drysolid basis, to the weight of raw rice grains before soaking in water,is sifted over unpolished- or polished-rice grains, and the mixture wasstirred uniformly. Trehalose or maltitol can be used in the form of apowder or solution. In the case of sifting powdery trehalose or maltitolover rice grains, the sifted saccharide melts on the surface of ricegrains and then penetrates into unpolished rice grains through thecracks formed by crushing or into polished rice grains through thesurface increased in area by rough crushing. In the case of spraying asolution containing trehalose or maltitol on rice grains, the solutionpenetrates unpolished- or polished-rice grains through the abovementioned routes. Although the time for penetrating trehalose ormaltitol into rice grains is different depending on the process usedwith heating or not; 30-60 minutes would be sufficient. Origin oftrehalose or maltitol used in the process is not restricted. Forexample, hydrous crystalline trehalose obtainable from starch byenzymatic saccharification, disclosed in Japanese Patent Kokai No.170,977/95, and anhydrous crystalline maltitol obtainable byhydrogenating maltose, disclosed in Japanese Patent No. 2,439/88, can beadvantageously used. Commercialized trehalose and maltitol products canbe also used. For example, “TREHA®”, a high purity hydrous crystallinetrehalose product (trehalose content: 98.0% or higher) and “FUNMATSUMABIT®”, a maltitol powder (maltitol content: 93.5% or higher), bothcommercialized by Hayashibara Shoji Inc., Okayama, Japan, can beadvantageously used.

Using rice flour obtainable by penetrating trehalose or maltitol intorice grains for producing bakery products, fermented bread having asatisfactory bulk can be obtained as described later. While, fermentedbread having an unsatisfactory bulk is obtained by using rice flourproduced without the saccharide-penetration process. From the aboveresults, it is supposed that the damage of rice flour starch, which isoccurred by milling, is suppressed by penetrating trehalose or maltitolinto material rice grains.

The applicant disclosed in Japanese Patent Kokai No. 123,194/2001 thatthe formation of volatile aldehydes from fatty acids contained in branor embryo and the generation of “smell of rice bran”, so-called, arestrongly suppressed by incorporating trehalose and/or maltitol intounpolished rice grains in the cases of polishing unpolished rice andproducing pre-washed rice because they suppress the decomposition offatty acids per se; and polished rice and pre-washed rice, both having ahigh quality, can be produced. The penetration of trehalose or maltitolinto rice grains in the present process for producing rice flour leadsincorporates trehalose or maltitol into rice flour products. Therefore,it is preferable for suppressing “smell of rice bran”, which isoriginated from bran and/or embryo contained in rice flour products.

Rice grains, produced by penetrating trehalose or maltitol, arepartially dried before milling. The partial drying as referred to as inthe present invention means that rice grains, produced by penetratingtrehalose or maltitol and having a moisture content of about 30%, isdried to give a moisture content of 14-25%. In the case of using ricegrains having a moisture content of higher than 25%, it hinders to theoperation of milling machine because it increases the formation ofadhesive rice flour in the process of milling. In the case of using ricegrains having a moisture content of lower than 14%, rice flour having amoisture content of lower than 8% is produced by evaporating during themilling process without causing any problem for milling. However, suchrice flours have unsatisfactory processing properties and gives breadhaving an unsatisfactory bulk at the test for producing bakery productsdescribed later. The partial drying can be done after or in parallelwith the penetration of trehalose or maltitol into rice grains. Thepartial drying of rice grains is preferably done at temperatures oflower than 60° C.

The rice grains obtained by the partial drying can be easily milled byconventional milling methods such as roll-, impact-, and stamp-millings.Although such milling machines are not specifically restricted, it isdesirable to use a machine which gives rice flour having an averageparticle size of 30-80 μm and a narrow particle size distribution asmuch as possible, as regard to the processing properties (qualities forproducing bakery products) as described later. Further, for producingrice flour having a high quality, it is desirable to collect rice flourhaving the above average particle size by sieving. Furthermore, it isdesirable to adjust the moisture content of final rice flour product to,usually, 8-16%, preferably, 10-14%. Rice flours having a small averageparticle size or that dried to give a moisture content of lower than 8%show unsatisfactory processing properties, especially, unsatisfactoryqualities in producing bakery products.

In the case of using unpolished rice as a material, rice flour producedby the present invention is a high quality unpolished rice flour rich innutritional components such as amino acids, vitamins, minerals, etc.,and having a suppressed smell of rice bran. In the case of usingpolished rice as a material, rice flour produced by the presentinvention is a high quality polished rice flour having a pure whitecolor similar to “JOSHINKO” and “JOYOKO” and having a suppressed smellof rice bran. The both unpolished- and polished-rice flours havesatisfactory processing properties and can be advantageously used asmaterials for premixed flours for producing bakery products, fermentedbakery products, and noodles.

The following experiments concretely explain the present invention:

EXPERIMENT 1 Studies on Processes for Producing Rice Flour andEvaluation of the Qualities of Rice Flours Obtained Thereby

In order to investigate the effects of the process of crushing andpenetrating saccharides into rice and the moisture content of rice flourproducts on the quality of rice flour, five kinds of rice flours wereproduced by five different processes, which are different in process ofcrushing and penetrating saccharides into rice grains and the moisturecontents of rice, and evaluated their qualities in the followingExperiments 1-1 to 1-4. Further, in order to evaluate the qualities ofthese rice flours, their properties in producing bakery products wereinvestigated by following test.

[Process for Producing Rice Flour]

Forty kilograms of unpolished- or polished-rice grains, a domesticvariety of “AKEBONO”, was soaked into 80 L of water for 16 hours forallowing to absorb water and then being washed with water to removeimpurities. The resulting rice grains were divided into five portions,and five kinds of rice flours were produced according to the processesshown in Table 1, respectively. TABLE 1 Process Process Process ProcessProcess Process 1 2 3 4 5 Soaking in water Done Done Done Done DoneCrushing ND* Done ND Done Done Saccharide-penetrating ND ND Done DoneDone Partial drying Done Done Done Done Done Milling Done Done Done DoneDone Final moisture content 8-16 8-16 8-16 Less 8-16 of rice flour (%)than 8*ND; Not done

Crushing treatment of rice was done using “SUZUKI NOODLE MAKINGMACHINE”, a roll-type noodle making machine commercialized bySuzukimenko Co., Ltd., Okayama, Japan, whose slit width was adjusted toone millimeter for unpolished rice, or two millimeter for polished rice.Saccharide-penetrating treatment was carried out by the steps of siftingtrehalose or maltitol over the grains in an amount of 10% (w/w) to thematerial rice grains and keeping the mixture at ambient temperature for50 minutes with gentle stirring. “TREHA®”, a high purity hydrouscrystalline trehalose product (trehalose content: 98.0% or higher) and“FUNMATSU MABIT®”, a maltitol powder (maltitol content: 93.5% orhigher), both commercialized by Hayashibara Shoji Inc., Okayama, Japan,were used as trehalose and maltitol, respectively. After penetratingeither of the saccharide into rice grains, the resulting grains werepartially dried by heating at 60° C. for four hours to give a moisturecontent of about 24%. The resulting partially-dried rice grains weremilled using “TORNADO MILL”, a dry-type micro-pulverizing millcommercialized by Nikkiso Co., Ltd., Tokyo, Japan, whose outlettemperature was controlled at 60° C., and a fine rice flour having anaverage particle size of 30-60 mm was collected by sieving with asifter.

The average particle size, moisture content, and smell of rice bran wereinvestigated as the evaluation items of fine rice flour. The averageparticle size of rice flour was measured using “Model SA-CP3L”, acentrifugal sedimentation-type particle size distribution analyzercommercialized by Shimadzu Corporation, Kyoto, Japan. The moisturecontent of rice flour was measured by the aforesaid drying by heatingmethod. The smell of rice bran of rice flour was evaluated by the stepsof putting any of the prepared rice flours into a polyethylene bag,preserving it at ambient temperature for 10 days under a sealedcondition, and then smelling by twenty panelists. The results ofevaluation of rice flours, which showed the smell of rice bran clearly,slightly, and hardly, were expressed with the symbols “C”, “S”, and “H”,respectively.

[Test for Evaluating the Quality of Rice Flour for Bakery Products]

One hundred parts by weight any of the rice flours obtained above, 15parts by weight of “GLURICH A ”, a gluten commercialized by Chiba SeifunCo. Ltd., Chiba, Japan, two parts by weight of “TREHA®”, a trehaloseproduct (trehalose content of 98.0% or higher) commercialized byHayashibara Shoji Inc., Okayama, Japan, three parts by weight ofsucrose, two parts by weight of sodium chloride, 10 parts by weight ofsweet butter, two parts by weight of “KAIYO KOBO”, a yeastcommercialized by Sankyo Foods Co., Ltd., Tokyo, Japan, two parts byweight of “RULLULAN PF-20”, a pullulan product commercialized byHayashibara Shoji Inc., Okayama, Japan, and 75 parts by weight of waterwere kneaded by a kneader at 25° C. for five minutes at a low speed andfor six minutes at a moderate speed. After suspending the kneading for awhile, the mixture was further kneaded for four minutes to make into adough. As regard to the rice flours produced by Processes 1 and 2,trehalose or maltitol was not incorporated thereunto because the twokinds of rice flours were produced without saccharide-penetrationprocess. Therefore, in the case of rice flours obtained by Process 1 and2, 90 parts by weight of any of rice flours and 10 parts by weight oftrehalose or maltitol were used instead of using 100 parts by weight ofthe rice flour corresponding to the above material composition, for thepurpose of equalizing the amount of saccharide among five kinds ofdoughs. After preparing doughs, they were fermented for 50 minutes asfloor time”. After dividing the fermented doughs, they were rounded andfermented for 20 minutes as “bench time”. Successively, the resultingdoughs were placed in tins having a height of 3.5 cm to shape into anopen top bread and further fermented for 50 minutes using a proofingroom controlled at 40° C. and a humidity of 80%. After the fermentation,the doughs were baked for 45 minutes in an oven which the upper andlower temperatures were controlled at 230° C. and 200° C., respectively,to produce rice flour open top breads. Properties of the rice flours forproducing bakery products were evaluated by measuring the bulk of theopen top bread obtained above and examining the taste by twentypanelists. The bread showing a bad- or good taste was expressed with “Nogood” or “Good, and the results are in Tables. Further, as an overallevaluation, rice flours showing unsatisfactory smell of rice bran andproperties for producing bakery products (bulk and taste) were expressedwith “No good”. Also, that showing unsatisfactory smell of rice bran orthe properties was expressed with “Good”. The rice flour showing bothsatisfactory results was expressed with “Better”.

EXPERIMENT 1-1 Rice Flour Produced from Unpolished Rice Using Trehalose

Five kinds of unpolished rice flours were produced by the aforesaidprocesses for producing rice flours using a select domestic unpolishedrice of a variety of “AKEBONO” as a material, and their qualities wereevaluated by the test for the properties for producing bakery products.The results are in Table 2. Unpolished rice flours 1, 2, 3, 4, and 5 inTable 2 mean the unpolished rice flours produced by the processes of 1,2, 3, 4, and 5, respectively. TABLE 2 Evaluation URF*1 URF2 URF3 URF4URF5 Analytic APS**(μm) 52 56 55 51 54 data of MC*** (%) 9.6 10.1 10.36.7 12.4 rice flour SRB**** C C H H H Properties Bulk (cm) 9.1 9.3 9.010.5 11.8 for bakery Taste No No No Good Good products good good goodOverall evaluation No No No Good Better good good good*Unpolished rice flour**Average particle size***Moisture content****Smell of rice bran

As shown in Table 2, unpolished rice flour 1 produced without theprocesses of crushing and trehalose-penetration showed a distinct smellof rice bran. The quality of unpolished rice flour 1 was evaluated to beunsatisfactory because the rice flour gave a bread with a relativelysmall bulk and unsatisfactory bulge and taste based on the evaluation ofthe properties for producing bakery products. Unpolished rice flour 2,produced with crushing but not with trehalose-penetration, showedunsatisfactory qualities as in the case of unpolished rice flour 1.Unpolished rice flour 3, produced with trehalose-penetration but notwith crushing, showed a suppressed smell of rice bran by incorporatingtrehalose. However, the rice flour showed unsatisfactory qualities forproducing bakery products as in the case of using unpolished rice flour1 and 2. The reason of this was considered that trehalose did notpenetrate sufficiently into unpolished rice grains when rice flour wasproduced with trehalose-penetration and without crushing, becauseunpolished rice grains have a hard outer layer such as cuticle, testa,and pericarp. While, unpolished rice flours 4 and 5, both produced withcrushing and trehalose-penetration, showed a suppressed smell of ricebran and gave fermented breads having a good taste. However, unpolishedrice flour 5, having a relatively high moisture content of 12.4%,imparted a better quality to a fermented bread having a large bulk thanin the case of using unpolished rice flour 4, having a relatively lowmoisture content of 6.7%.

EXPERIMENT 1-2 Rice Flour Produced From Polished Rice Using Trehalose

Except for using a domestic polished rice grains of a variety of“AKEBONO”, five kinds of polished rice flours were produced according tothe procedure described in Experiment 1-1 and evaluated on theirqualities including those for producing bakery products. The results arein Table 3. The polished rice flours 1, 2, 3, 4, and 5 in Table 3 meanthose produced by the processes of 1, 2, 3, 4, and 5, respectively.TABLE 3 Evaluation PRF*1 PRF2 PRF3 PRF4 PRF5 Analytic APS**(μm) 40 38 3545 48 data of MC*** (%) 10.5 9.8 9.3 6.3 12.8 rice flour SRB**** S S H HH Properties Bulk (cm) 9.0 9.2 10.5 11.0 12.5 for bakery Taste No NoGood Good Good products good good Overall evaluation No No Good GoodBetter good good*Polished rice flour**Average particle size***Moisture content****Smell of rice bran

As shown in Table 3, polished rice flour 1, produced without theprocesses of crushing and trehalose-penetration, showed a slight smellof rice bran. The quality of polished rice flour 1 was evaluated asunsatisfactory because it gave bread with a relatively small bulk andunsatisfactory bulge and taste when evaluated with respect to theproperties for producing bakery products. Polished rice flour 2,produced with crushing but not with trehalose-penetration, showedunsatisfactory qualities as in the case of polished rice flour 1.Polished rice flour 3, produced with trehalose-penetration but not withcrushing, showed almost no smell of rice bran. Although the rice flourgave bread having a good taste, the bulk of which was unsatisfactory.The reason of this was considered that trehalose did not penetratesufficiently into the polished rice grains because the polished riceflour was produced without crushing. On the other hand, polished riceflours 4 and 5, both produced with crushing and trehalose-penetration,showed a suppressed smell of rice bran and gave fermented bread having agood taste. However, polished rice flour 5, having a relatively highmoisture content of 12.8%, showed a better quality of giving fermentedbread having a large bulk than those prepared with polished rice flour4, having a relatively low moisture content of 6.3%.

EXPERIMENT 1-3 Rice Flour Produced From Unpolished Rice Using Maltitol

Except for using maltitol instead of trehalose as a saccharide forpenetration, five kinds of unpolished rice flours were producedaccording to the procedure described in Experiment 1-1 and evaluated thequalities including the properties for producing bakery products. Theresults are in Table 4. Unpolished rice flours 1, 2, 3, 4, and 5 inTable 4 mean those produced by the processes of 1, 2, 3, 4, and 5,respectively. TABLE 4 Evaluation URF*1 URF2 URF3 URF4 URF5 AnalyticAPS**(μm) 42 46 55 53 51 data of MC*** (%) 10.4 11.1 10.3 6.1 13.2 riceflour SRB**** C C H H H Properties Bulk (cm) 9.0 9.2 9.0 10.5 12.0 forbakery Taste No No No Good Good products good good good Overallevaluation No No No Good Better good good good*Unpolished rice flour**Average particle size***Moisture content****Smell of rice bran

As shown in Table 4, unpolished rice flour 1, produced without theprocesses of crushing and maltitol-penetration showed a strong smell ofrice bran. The quality of unpolished rice flour 1 was evaluated asunsatisfactory because it gave bread showing a relatively small bulk andunsatisfactory bulge and taste when evaluated with respect to theproperties for producing bakery products. Unpolished rice flour 2,produced with crushing but not with maltitol-penetration, showedunsatisfactory qualities as in the case of unpolished rice flour 1.Unpolished rice flour 3, produced with maltitol-penetration but not withcrushing, showed a suppressed smell of rice bran by incorporatingmaltitol. However, the rice flour showed unsatisfactory qualities forproducing bakery products as in the case of unpolished rice flour 1 and2. The reason of this was considered that maltitol did not penetratesufficiently into the unpolished rice grains when rice flour wasproduced with maltitol-penetration and without crushing becauseunpolished rice grains have a hard outer layer such as cuticle, testa,and pericarp. On the other hand, unpolished rice flours 4 and 5, bothproduced with crushing and maltitol-penetration, showed a suppressedsmell of rice bran and gave fermented bread having a good taste.However, unpolished rice flour 5, having a relatively high moisturecontent of 13.2%, showed a better quality of giving fermented breadhaving a large bulk than those prepared with unpolished rice flour 4,having a relatively low moisture content of 6.1%.

EXPERIMENT 1-4 Rice Powder Produced From Polished Rice Using Maltitol

Except for using a domestic polished rice grains of a variety of“AKEBONO”, and maltitol instead of trehalose, five kinds of polishedrice flours were produced according to the procedure described inExperiment 1-1 and evaluated their qualities of including the propertiesfor producing bakery products. The results are in Table 5. Polished riceflours 1, 2, 3, 4, and 5 in Table 5 mean those produced by the processesof 1, 2, 3, 4, and 5, respectively. TABLE 5 Evaluation PRF*1 PRF2 PRF3PRF4 PRF5 Analytic APS**(μm) 39 35 38 45 43 data of MC*** (%) 10.5 9.89.3 5.9 12.8 rice flour SRB**** S S H H H Properties Bulk (cm) 10.3 10.110.5 11.0 11.2 for bakery Taste No No Good Good Good products good goodOverall evaluation No No Good Good Better good good*Polished rice flour**Average particle size***Moisture content****Smell of rice bran

As shown in Table 5, polished rice flour 1 produced without theprocesses of crushing and maltitol-penetration showed a slight smell ofrice bran. The quality of polished rice flour 1 was evaluated asunsatisfactory because it gave bread showing a relatively small bulk andunsatisfactory bulge and taste when evaluated with respect to theproperties for producing bakery products. Polished rice flour 2,produced with crushing but not with maltitol-penetration, showedunsatisfactory qualities as in the case of polished rice flour 1.Polished rice flour 3, produced with maltitol-penetration but not withcrushing, showed almost no smell of rice bran. Although the rice flourgave bread having a good taste, the bulk of which was unsatisfactory.The reason of this was considered that maltitol did not penetratesufficiently into the polished rice grain because they were producedwithout-crushing. On the other hand, polished rice flours 4 and 5, bothproduced with crushing and maltitol-penetration, showed a suppressedsmell of rice bran and gave fermented bread having a good taste.However, polished rice flour 5, having a relatively high moisturecontent of 12.8%, showed a better quality of giving fermented breadhaving a large bulk than those prepared with polished rice flour 4,having a relatively low moisture content of 5.9%.

The following examples concretely explain the present invention.Examples A explain the production of rice flours. Further, Examples Bexplain the preparation of premixed flours for producing bakery productsand bakery products obtained by using those flours:

EXAMPLE A-1 Production of Rice Flour From Unpolished Rice

Unpolished rice grains of a domestic variety of “AKEBONO” were soaked intwo-folds by weight of water for 16 hours for allowing to absorb waterand then washed with water to remove impurities. Successively, crackedrice grains were prepared by subjecting the resulting rice grains to“SUZUKI NOODLE MAKING MACHINE”, a roll-type noodle making machinecommercialized by Suzukimenko Co., Ltd., Okayama, Japan, whose slitwidth was adjusted to 1.5 mm, for crushing. Then, “TREHA®”, a highpurity hydrous crystalline trehalose product (trehalose content: 98.0%or higher) commercialized by Hayashibara Shoji Inc., Okayama, Japan, waspenetrated into the rice grain by sifting the saccharide over the grainsin an amount of 10% to the weight of the material rice grains andkeeping the mixture at ambient temperature for 50 minutes with gentlestirring. Successively, the resulting unpolished rice grains werepartially dried by heating at 60° C. for four hours to give a moisturecontent about 24%. The resulting partially-dried unpolished rice grainswere milled using “TORNADO MILL”, a dry-type micro-pulverizing millcommercialized by Nikkiso Co., Ltd., Tokyo, Japan, whose outlettemperature was controlled at 60° C., and the resulting fine unpolishedrice flour, having an average particle size of 60 μm and a moisturecontent of 13%, was collected by sieving with a sifter. The unpolishedrice flour thus obtained is rich in amino acids, vitamins, and minerals,and it has a satisfactory quality with a suppressed smell of rice branbecause of the incorporation of trehalose. Thus, the product can beadvantageously used as materials for various processed foods such asbakery products and noodles.

EXAMPLE A-2 Production of Rice Flour From Polished Rice

Polished rice grains of a domestic variety of “AKEBONO” were soaked inthree-folds by weight of water for eight hours for allowing to absorbwater and then washed with water to remove impurities. Successively, theresulting polished rice grains were roughly crushed using “Three-rollMill type S”, a roll-type milling machine commercialized by InoueSeisakusho Co., Ltd., Kanagawa, Japan, whose slit width was adjusted to2.5 mm. Then, trehalose was penetrated into the roughly crushed ricegrains by uniformly spraying 30% (w/w) aqueous solution of “TREHA®”, ahigh purity hydrous crystalline trehalose product (trehalose content:98.0% or higher) commercialized by Hayashibara Shoji Inc., Okayama,Japan, in an amount of 30% to the weight of the material rice grains andkeeping for 45 minutes with gentle stirring. Successively, the resultingroughly crushed polished rice grains were partially dried by heating at50° C. for 10 hours to give a moisture content of about 18%. Theresulting partially-dried polished rice grains were milled using“Three-roll Mill type S”, a roll-type milling machine commercialized byInoue Seisakusho Co., Ltd., Kanagawa, Japan. After partially drying theresulting rice flour to give a moisture content of 10%, fine polishedrice flour having an average particle size of 80 μm was collected bysieving with a sifter. The polished rice flour thus obtained has asatisfactory quality with a suppressed smell of rice bran because of theincorporation of trehalose. Thus, the product can be advantageously usedas materials for various processed foods such as bakery products andnoodles.

EXAMPLE A-3 Production of Rice Flour From Unpolished Rice

Select unpolished rice grains of domestic variety of “HINOHIKARI” weresoaked in three-folds by weight of water for 16 hours for allowing toabsorb water and then washed with water to remove impurities.Successively, cracked rice grains were prepared by subjecting theresulting rice grains to “SUZUKI NOODLE MAKING MACHINE”, a roll-typenoodle making machine commercialized by Suzukimenko Co., Ltd., Okayama,Japan, whose slit width was adjusted to 1.5 mm, for crushing. Then,maltitol was penetrated into the cracked rice grains by uniformlyspraying 30% (w/w) aqueous solution of “FUNMATSU MABIT®”, a powderymaltitol product (maltitol content: 93.5% or higher) commercialized byHayashibara Shoji Inc., Okayama, Japan, in an amount of 30% to theweight of material rice and keeping for 45 minutes with gentle stirring.Successively, the resulting unpolished rice grains were partially driedby heating at 60° C. for four hours to give a moisture content of about22%. The resulting partially-dried unpolished rice grains were milledusing “Three-roll Mill type S”, a roll-type milling machinecommercialized by Inoue Seisakusho Co., Ltd., Kanagawa, Japan. Afterdrying the resulting unpolished rice flour to give a moisture content of13%, and fine unpolished rice flour having an average particle size of80 μm was collected by sieving with a sifter. Unpolished rice flour thusobtained is rich in amino acids, vitamins, and minerals, and has asatisfactory quality with a suppressed smell of rice bran because of theincorporation of maltitol. Thus, the product can be advantageously usedas materials for various processed foods such as bakery products andnoodles.

EXAMPLE A-4 Production of Rice Flour From Polished Rice

Polished rice grains of a domestic variety of “ASAHI” were soaked intwo-folds by weight of water for eight hours for allowing to absorbwater and then washed with water to remove dirt impurities.Successively, the resulting polished rice grains were roughly crushedusing “Three-roll Mill type S”, a roll-type milling machinecommercialized by Inoue Seisakusho Co., Ltd., Kanagawa, Japan, whoseslit width was adjusted to 2.5 mm. Then, “FUNMATU MABIT”, a powderymaltitol product (maltitol content: 93.5% or higher) commercialized byHayashibara Shoji Inc.,, Okayama, Japan, was penetrated into the roughlycrushed rice grains by sifting the saccharide over the grains in anamount of 10% to the weight of the material rice grains and keeping atroom temperature for 60 minutes with gentle stirring. Successively, theresulting polished rice grains was partially dried by heating at 50° C.for 10 hours to give a moisture content of about 15%. The resultingpartially-dried polished rice grains were milled using “TORNADO MILL”, adry-type micro-pulverizing mill commercialized by Nikkiso Co., Ltd.,Tokyo, Japan. After partially drying the resulting rice flour to give amoisture content of 12%, fine polished rice flour having an averageparticle size of 70 μm was collected by sieving with a sifter. Polishedrice flour thus obtained has a satisfactory quality with a suppressedsmell of rice bran because of the incorporation of maltitol. Thus, theproduct can be advantageously used as materials for various processedfoods such as bakery products and noodles.

EXAMPLE B-1 Premixed Flour for Producing Bakery Products With Rice Flour

One hundred parts by weight of unpolished rice flour, obtained inExample A-1, 15 parts by weight of “GLURICH A”, a gluten commercializedby Chiba Seifun Co. Ltd., Chiba, Japan, five parts by weight of “SUNMALTS”, a purified maltose product (maltose content: 92.0% or higher)commercialized by Hayashibara Shoji Inc., Okayama, Japan, and one partby weight of “MAGIC FAT 250”, a powdery fat commercialized by MiyoshiOil & Fat Co., Ltd., Tokyo, Japan, were mixed using a blender to producea premixed flour for producing bakery products.

The premixed flour, comprising unpolished rice flour, is rich in aminoacids, vitamins, and minerals and can be advantageously used forproducing bakery products being richin nutritional value. Further, sincethe unpolished rice flour contains trehalose, it can be expected thatthe generation of smell of rice bran will be suppressed when thepremixed flour is preserved for a long time.

EXAMPLE B-2 Premixed Flour for Producing Bakery Products With Rice Flour

One hundred parts by weight of polished rice flour, obtained in ExampleA-2, 20 parts by weight of “GLURICH A”, a gluten commercialized by ChibaSeifun Co. Ltd., Chiba, Japan, two parts by weight of “TREHA®”, a highpurity hydrous crystalline trehalose (trehalose content: 98.0% orhigher) commercialized by Hayashibara Shoji Inc., Okayama, Japan, fourparts by weight of “FUNMATSU MABIT”, a maltitol product (maltitolcontent: 93.5% or higher) commercialized by Hayashibara Shoji Inc.,Okayama, Japan, three parts by weight of “PULLULAN PF-20”, a pullulanproduct commercialized by Hayashibara Shoji Inc., Okayama, Japan, weremixed using a blender to produce a premixed flour for producing bakeryproducts.

The premixed flour can be advantageously used for producing fermentedbakery products. Further, since the premixed flour contains trehaloseand maltitol, it can be expected that the generation of smell of ricebran will be suppressed when the premixed flour is preserved for a longtime.

EXAMPLE B-3 Unpolished Rice Flour Bread

Seventy two parts by weight of unpolished rice flour, obtained inExample A-1, 8 parts by weight of “GLURICH A”, a gluten commercializedby Chiba Seifun Co. Ltd., Chiba, Japan, four parts by weight of“TREHA®”, a high purity hydrous crystalline trehalose (trehalosecontent: 98% or higher) commercialized by Hayashibara Shoji Inc.,Okayama, Japan, 1.6 parts by weight of sodium chloride, 2.4 parts byweight of sucrose, 2.4 parts by weight of skim milk, two parts by weightof “KAIYO KOBO”, a yeast commercialized by Sankyo Foods Co., Ltd.,Tokyo, Japan, 1.6 parts by weight of “PULLULAN PF-20”, a pullulanproduct commercialized by Hayashibara Shoji Inc., Okayama, Japan, fourparts by weight of butter and 64 parts by weight of water were kneadedby a kneader at 23° C. for six minutes at a low speed and for threeminutes at a moderate speed. After suspending the kneading for a while,the mixture was further kneaded for four minutes to make into a dough.Successively, the dough was fermented for 50 minutes as “floor time”.After dividing and rounding the dough, the dough was fermented for 20minutes as “bench time”. Then, the dough was placed in a tin to shapeinto open top bread and further fermented for 50 minutes using aproofing room controlled at 40° C. and a humidity of 80%. After thefermentation, the dough was baked for 45 minutes in an oven which theupper and lower temperatures were controlled to 230° C. and 200° C.,respectively, to produce unpolished rice flour-open top bread.

The unpolished rice flour-open top bread, obtained by the presentExample, showed a satisfactory bulk and taste. Since the bread wasproduced from unpolished rice flour, the bread was rich in amino acids,vitamins, minerals and nutritional value. Further, since the breadcomprised trehalose, it was a high quality bread whose smell of ricebran was suppressed.

EXAMPLE B-4 Polished Rice Flour Bread

Eighty parts by weight of polished rice flour, obtained in Example A-2,eight parts by weight of “GLURICH A”, a gluten commercialized by ChibaSeifun Co. Ltd., Chiba, Japan, 10 parts by weight of sucrose, 1.8 partsby weight of sodium chloride, two parts by weight of skim milk, twoparts by weight of “KAIYO KOBO”, a yeast commercialized by Sankyo FoodsCo., Ltd., Tokyo, Japan, two parts by weight of “CELLOGEN”, acarboxymethyl-cellulose sodium salt commercialized by Dai-ichi KogyoSeiyaku Co., Ltd., Kyoto, Japan, 10 parts by weight of fresh cream, fiveparts by weight of sugar-free condensed milk, four parts by weight ofshortening, and 80 parts by weight of water were kneaded by a kneader at23° C. for six minutes at a low speed and for three minutes at amoderate speed. After suspending the kneading for a while, the mixturewas further kneaded for four minutes to make into dough. Successively,the dough was fermented for 60 minutes as “floor time”. After dividingand rounding the dough, the dough was fermented for 20 minutes as “benchtime”. Then, the dough was placed in a tin to shape into open top breadand further fermented for 50 minutes using a proofing room controlled at40° C. and a humidity of 80%. After the fermentation, the dough wasbaked for 45 minutes in an oven which the upper and lower temperatureswere controlled to 230° C. and 200 ° C., respectively, to producepolished rice flour-open top bread.

The polished rice flour-open top bread, obtained by the present Example,showed a satisfactory bulk and taste. Further, since the bread comprisedtrehalose, it was a high quality bread whose smell of rice bran wassuppressed.

EXAMPLE B-5 Rice Flour Chinese Steamed Bread

One hundred thirty parts by weight of a premixed flour for producingrice flour bakery products, obtained in Example B-2, five parts byweight of sucrose, two parts by weight of “KAIYO KOBO”, a yeastcommercialized by Sankyo Foods Co., Ltd., Tokyo, Japan, two parts byweight of skim milk, two parts by weight of lard, 1.5 parts by weight ofbaking powder for steaming, and 90 parts by weight of water were kneadedby a kneader at 24° C. for six minutes at a low speed and for threeminutes at a moderate speed. After suspending the kneading for a while,the mixture was further kneaded for three minutes at a moderate speed tomake into a dough. Successively, the dough was fermented for 50 minutesas “floor time”. After dividing the dough into 50 grams each,cooked-ingredient was put into the dough and the dough was shaped. Then,the dough was fermented at room temperature for 40 minutes. After thefermentation, the resulting dough was steamed for 10 minutes over highflame using a steamer to make into rice flour Chinese bread.

The rice flour Chinese bread, obtained by the present Example, showed asatisfactory bulk and taste. Further, since the bread comprisedtrehalose, it was a high quality Chinese bread whose smell of rice branwas suppressed.

EXAMPLE B-6 Rice Flour Noodle

Eighty parts by weight of polished rice flour, obtained in Example A-4,eight parts by weight of “GLURICH A”, a gluten commercialized by ChibaSeifun Co. Ltd., Chiba, Japan, 4.5 parts by weight of sodium chloride,and 35 parts by weight of water were kneaded and prepared into dough fornoodles by conventional method. Then, noodle with a thickness of 0.9 mmwas prepared. The resulting noodle was boiled for five minutes andcooled to make into rice flour noodle.

The rice flour noodle, obtained by the present Example, showed asatisfactory taste. Further, since the noodle comprised maltitol, it wasa high quality rice flour noodle whose smell of rice bran wassuppressed.

INDUSTRIAL APPLICABILITY

According to the process for producing rice flour of the presentinvention, satisfactory rice flours can be produced efficiently, on anindustrial scale and at a lower cost independently of the kind ofmaterial rice such as unpolished, polished, and sprouted rice, using asingle method. Also, high quality rice flours, having a satisfactoryprocessing property for processed rice flour products, can be obtainedby the process. Further, rice flours, whose smell of bran originatedfrom bran and germ which contained in the rice flour product of thepresent invention were suppressed, can be produced by allowing toincorporate trehalose into material rice flours. Furthermore, since theprocess can be used for producing flours of other cereals as well asrice, it can be applied to the production of various cereal flours.

1. A process for producing rice flour, which comprises the steps of:soaking material rice grains in water; crushing the rice grains;penetrating α,α-trehalose or maltitol into the crushed rice grains;partially drying the resulting rice grains; and milling the partiallydried rice grains to produce a rice flour.
 2. The process of claim 1,wherein said material rice grains are raw rice grains selected from thegroup consisting of unpolished, polished, and sprouted rice grains. 3.The process of claim 1, wherein the crushing step is for cracking saidunpolished rice grains or roughly crushing said polished rice grains. 4.The process of claim 1, wherein the penetration step is done by using3-20% (w/w) of α,-trehalose or maltitol to the weight of said materialraw rice grains.
 5. The process of claim 1, wherein the penetration stepis done by using α,α-trehalose or maltitol in the form of a powder orsolution.
 6. The process of claim 1, the moisture content of rice in thepartially drying step is controlled to 14-25% (w/w).
 7. The process ofclaim 1, which further contains a step of sieving rice flour to give anaverage particle size of 30-80 μm.
 8. The process of claim 1, whereinsaid rice flour is processed for producing bakery products or noodles.9. A rice flour obtainable by the process of claim
 1. 10. A premixedflour for producing bakery products, comprising the rice flour of claim9.
 11. A fermented bakery product or noodle obtainable by using the riceflour of claim
 9. 12. The process of claim 2, wherein the crushing stepresults in cracking said unpolished rice grains or roughly crushing saidpolished rice grains.
 13. The process of claim 12, wherein thepenetration step is done by using 3-20% (w/w) of α,-trehalose ormaltitol to the weight of said material raw rice grains.
 14. The processof claim 13, wherein the penetration step is done by using α,α-trehaloseor maltitol in the form of a powder or solution.
 15. The process ofclaim 14, the moisture content of rice in the partially drying step iscontrolled to 14-25% (w/w).
 16. The process of claim 15, which furthercontains a step of sieving rice flour to give an average particle sizeof 30-80 μm.
 17. The process of claim 16, wherein said rice flour isprocessed for producing bakery products or noodles.
 18. A rice flourobtainable by the process of claim
 17. 19. A premixed flour forproducing bakery products, comprising the rice flour of claim
 18. 20. Afermented bakery product or noodle obtainable by using the rice flour ofclaim 18.